Flip light emitting diode chip and method of fabricating the same

ABSTRACT

A method of fabricating a light emitting diode device comprises providing a substrate, growing an epitaxial structure on the substrate. The epitaxial structure includes a first layer on the substrate, an active layer on the first layer and a second layer on the active layer. The method further comprises depositing a conductive and reflective layer on the epitaxial structure, forming a group of first trenches and a second trench. Each of the first and second trenches extends from surface of the conductive and reflective layer to the first layer to expose part of the first layer. The method further comprises depositing conductive material to cover a portion of the conductive and reflective layer to form a first contact pad, and cover surfaces between adjacent first trenches to form a second contact pad. The second contact pad electrically connects the first layer by filling the conductive material in the first trenches.

TECHNICAL FIELD

The example embodiments of the present invention generally relate to light emitting diodes device, and more particularly to flip light emitting diode chips and method of fabricating the same.

BACKGROUND

There are two fundamental ways to envisage light emitting diode chips, i.e., a lateral and a vertical die structure. FIG. 1( a) shows a lateral light emitting diode chip 100 of the prior art. FIG. 1( b) illustrates the lateral light emitting diode chip 100 assembled to a printed circuit board 160. With reference to FIG. 1( a), the lateral light emitting diode chip 100 includes a substrate 102, an n-type GaN layer 104 on the substrate 102, an active layer 106 on the n-type GaN layer 104, a p-type GaN layer 108 on the active layer 106, and contact pads 110 on the n-type GaN layer 104 and the p-type GaN layer 108 respectively. As shown in FIGS. 1( a) and 1(b), when the light emitting diode chip 100 is assembled to the printed circuit board 160, a lead frame 114 connects the contact pads 110 of the light emitting diode chip 100 to contact pads 168 of the printed circuit board 160.

FIG. 2( a) illustrates a vertical light emitting diode chip 200 of the prior art. FIG. 2( b) illustrates the vertical light emitting diode chip 200 assembled to a printed circuit board of the prior art. Similar to the lateral structure, the vertical light emitting diode chip 200 includes a substrate 202, an n-type GaN layer 204 on the substrate 202, an active layer 206 on the n-type GaN layer 204, a p-type GaN layer 208 on the active layer 206, and a contact pad 210 on the p-type GaN layer 208. As shown in FIG. 2( b), a lead frame 214 connects the contact pads (not numbered) of the light emitting diode chip 200 to contact pads 268 of a printed circuit board (not numbered).

As the light emitting diode chips (100, 200) are wiring bonded to the printed circuit boards, the heat generated in the active region may propagate through the substrate (102, 202) before being dissipated into the printed circuit board.

BRIEF SUMMARY

According to one exemplary embodiment of the present invention, a method of fabricating a light emitting diode device comprises providing a substrate, growing an epitaxial structure on the substrate. The epitaxial structure includes a first layer on the substrate, an active layer on the first layer and a second layer on the active layer. The method further comprises depositing a conductive and reflective layer on the epitaxial structure, forming a group of first trenches and a second trench. Each of the first and second trenches extends from surface of the conductive and reflective layer to the first layer to expose part of the first layer. The method further comprises depositing conductive material to cover a portion of the conductive and reflective layer to form a first contact pad, and cover surfaces between adjacent first trenches to form a second contact pad. The second contact pad electrically connects the first layer by filling the conductive material in the first trenches. The first contact pad is spatially separated from the second contact pad by the second trench.

According to one exemplary embodiment of the present invention, a light emitting diode device comprises a substrate, an epitaxial structure grown on the substrate, a conductive layer deposited on the epitaxial structure. The epitaxial structure includes a first layer having a first material, an active layer on the first layer, the active layer having a second material and a second layer on the active layer. The second layer has the first material. The first layer and the second layer include different types of doping. The first material has wider band gap than that of the second material. The light emitting diode device further comprises a first contact pad formed on the conductive layer and a second contact pad covering surfaces between adjacent first trenches. The first contact pad is spatially separated from the second contact pad by a second trench. The second contact pad electrically connects to the first layer by filling conductive material in the first trenches. The first and second trenches extend from the conductive layer to the first layer to expose part of the first layer.

According to one exemplary embodiment of the present invention, a method of assembling a light emitting diode device to a metal core printed circuit board comprises electrically connecting the first and second contact pads of the light emitting diode device to first and second conductive pads of the metal core printed circuit board respectively, coupling a most upper layer to a mesa structure of the metal core printed circuit board.

BRIEF DESCRIPTION OF THE DRAWING(S)

Having thus described the example embodiments of the present invention in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein:

FIG. 1( a) illustrates a lateral light-emitting diode chip of the prior art;

FIG. 1( b) illustrates a lateral light-emitting diode chip assembled to a metal core printed circuit board;

FIG. 2( a) illustrates a vertical light-emitting diode chip of the prior art;

FIG. 2( b) illustrates a vertical light-emitting diode chip assembled to a metal core printed circuit board;

FIGS. 3( a)-3(f) are cross-sectional views to illustrate process of fabricating a flip light emitting diode chip according to one example embodiment of the present invention;

FIGS. 3( g)-3(h) are cross-sectional views to illustrate a flip light emitting diode chip having a single passivation layer assembled to a printed circuit board according to one example embodiment of the present invention;

FIG. 4( a) illustrates a 3-D view of trenches formed in FIG. 3( d);

FIGS. 4( b)-4(d) illustrate top views of exemplary trenches formed in FIG. 3( d).

FIGS. 5( a)-5(b) are cross-sectional views to illustrate an alternative example embodiment of FIGS. 3( f) and 3(g);

FIGS. 6( a)-6(b) are cross-sectional views to illustrate an alternative example embodiment of FIGS. 3( f) and 3(g);

FIGS. 7( a)- 7(e) are cross-sectional views to illustrate an alternative example embodiment of FIGS. 3( f)-3(h);

FIGS. 8( a)-8(b) are cross-sectional views to illustrate an alternative example embodiment of FIGS. 7( c)-7(d);

FIGS. 9( a)-9(b) are cross-sectional views to illustrate an alternative example embodiment of FIGS. 7( c)-7(d);

FIGS. 10( a)-10(d) are cross-sectional views to illustrate process of fabricating a flip light emitting diode chipset according to one example embodiment of the present invention; and

FIGS. 11( a)-11(b) illustrate cross-sectional views of assembling a light emitting diode chip to a printed circuit board according to example embodiments of the present invention.

DETAILED DESCRIPTION

The present disclosure now will be described more fully with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. This disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth; rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure . Like numbers refer to like elements throughout.

FIGS. 3( a)-3(f) are cross-sectional views that illustrate a method of fabricating a flip light emitting diode chip according to one example embodiment of the present invention. As illustrated in FIG. 3( a), the method includes growing an epitaxial structure 304 on a substrate 302. The epitaxial structure 304 may include a first layer 304 a, an active layer 304 b on the first layer 304 a and a second layer 304 c on the active layer 304 b. The first layer 304 a and the second layer 304 c may include a first material. The active layer 304 b may include a second material that has narrower band gap than that of the first material. The first layer 304 a and the second layer 304 c may include different types of doping. For instance, the first layer 304 a may be an n-doped semiconductor layer. The second layer 304 c may be a p-doped semiconductor layer. An additional layer, such as an adhesion layer, a seed layer or a buffer layer (not shown) may be deposited on the substrate 302 prior to the growth of the epitaxial structure 304 to improve the adhesion between the epitaxial structure 304 and the substrate 302.

The substrate 302 may include Al₂O₃ or any other insulating material such as SiC, ZnO, MgO, Ga₂O₃, AlGaN, GaLiO, AlLiO, or Si. In one embodiment, the active layer 304 b may include at least one of indium gallium nitride (InGaN), AlGaAs, GaP, AlInGaP, or GaAsP. The first and second layers 304 a and 304 c may include gallium nitride (GaN), or Gallium Arsenide (GaAs). The epitaxial structure 304 may be deposited on the substrate 302 by metal organic chemical vapor deposition (MOCVD) process or any other suitable deposition processes.

The method may further include depositing a conductive layer 310 on the epitaxial structure 304 as shown in FIG. 3( b). The conductive layer 310 may be deposited by metal film deposition methods such as physical vapor deposition (PVD). The conductive layer 310 may include at least one of conductive materials that have light reflection properties, such as Ag, Al, Rh, Ti, Ni, W, Mo, Cr, Pt and Pd. In an alternative embodiment, the conductive layer 310 may include at least one of materials that have translucent or transparent properties or insufficient reflective properties, such as In₂O₃, SnO₂, IMO, ZnO, IZO, ITO, Ni, Au, Ti or Ni.

An additional layer (not shown), such as an adhesion layer, a seed layer or a buffer layer, may be deposited on the epitaxial structure 304 prior to the deposition of the conductive layer 310. The additional layer may include at least one of conductive materials, such as Ti, Ni, Sn, Cr and WTi.

A photolithography process may then be applied to transfer a pattern on a photomask to a light-sensitive photoresistor. Reactive ion etching process may be used to selectively remove parts of the layers (304 a, 304 b, 304 c, 310) previously deposited on the substrate 302, resulting in a space 312 that extends from surface of the conductive layer 310 to the substrate 302 to expose part of the substrate 302, as shown in FIG. 3( c). The space 312 may separate adjacent light emitting diode dies that are described in detail in FIGS. 11( a) and 11(b) and may also be used to separate a die from a wafer in later packaging process.

Referring to FIG. 3( d), another photolithography and etching process may be applied to form a plurality of trenches (e.g., first trenches 314 a, a second trench 314 b) that extend from surface of the conductive layer 310 to the first layer 304 a to expose part of the first layer 304. The trenches may have different sizes in accordance with their uses. For instance, the second trench 314 b having a larger width may be used for isolating a contact pad from layers (304 b, 304 c, 310) in later fabrication process. The trench(es) with a smaller width(s), for example the first trenches 314 a, may be used for forming a contact pad connecting to the first layer 304 a in next step shown in FIG. 3( e). The first trenches 314 a may be in various forms. In an example embodiment, the first trenches 314 a may be in the form of columns. A 3D view and a top view of columns of the first trenches 314 a are illustrated in FIGS. 4( a) and 4(b), respectively. Alternatively, the first trenches 314 a may be in the form of grids as shown in FIG. 4( c) and/or meshes as shown in FIG. 4( d).

To form contact pads for the light emitting diode device, a layer of conductive material may be deposited on the surface of the wafer. A photolithography process may subsequently be applied to remove undesired conductive material to form a first contact pad 316 a and a second contact pad 316 b on the conductive layer 310. The first contact pad 316 a covers a portion of the conductive layer 310 on one side of the second trench 314 b. The second contact pad 316 b on the other side of the second trench 314 b covers surfaces of the conductive layer 310 between adjacent first trenches 314 a and electrically connects to the first layer 304 a by filling the conductive material in the first trenches 314 a, as shown in FIG. 3( e). The electric connections formed by the trenches 314 a between the second contact pad 316 b and the first layer 304 a may result in lower contact resistance and higher driving current, thus reducing heat generated on the first layer 304 a. The conductive material of the first contact pad 316 a and the second contact pad 316 b may include at least one of Ti, Ni, Au, Cr, Ag, Al, Cu and W.

A passivation layer may be deposited over the wafer followed by applying a photolithography process to remove undesired passivation material from the first and second contact pads 316 a and 316 b and obtain a desired thickness of the passivation layer. In one embodiment, the passivation layer, such as a passivation layer 318 shown in FIG. 3( f), may be formed at the same plane level as that of the first and second contact pads 316 a and 316 b.

Subsequent to the deposition of the passivation layer 318, the substrate may be chemically or mechanically polished to a desired thickness. The wafer may be diced into individual light emitting diode chip, resulting in a plurality of light emitting diode chips per wafer. In an assembly process illustrated in FIG. 3( g), a light emitting diode chip 330 is flipped over so that the contact pads 316 a and 316 b face down. To attach the flip light emitting diode chip 330 onto a metal core printed circuit board 340, conductive bonder 332, such as solder paste or conductive epoxy, are re-melted to produce an electric connection between the contact pads (316 a, 316 b) of the light emitting diode chip 330 and conductive pads (342 a, 342 b) of the metal core printed circuit board 340 using one of reflow solder process, thermal cure, ultrasonic and ultraviolet methods. On top surface the metal core printed circuit board 340 and between the two conductive pads 342 a and 342 b, a metal mesa structure 348 may physically contact the passivation layer 318 resulting in an acceleration of heat dissipation from the flip light emitting diode chip 330 to the metal core printed circuit board 340 in operation.

In an instance in which a metal core printed circuit board has no metal mesa structure, as a metal core printed circuit board 340′ shown in FIG. 3( h), there may be a space existing between the flip light emitting diode chip 330 and the metal core printed circuit board 340′. To couple the flip light emitting diode chip 330 to the metal core printed circuit board 340′, dielectric thermal-conductive material 344 may be filled in the space that may improve thermal dissipation. Alternatively, the coupling between the flip light emitting diode chip and the metal core printed circuit board may be made by altering the thickness of the passivation layer 318 during the deposition and photolithography processes.

Depending on the various heights of the metal mesa structure of the metal core printed circuit boards (including the embodiment that has no metal mesa structure) the passivation layer may be thicker or thinner than that illustrated in FIG. 3( f). In an example embodiment illustrated in FIGS. 5( a) and 5(b), because the surface of a metal mesa structure 548 of a metal core printed circuit board 540 is lower than that of the first and second contact pads 516 a and 516 b of a light emitting diode chip 530, a thicker passivation layer 518 may be formed to allow the metal mesa structure 548 to physically contact the passivation layer 518. In another example embodiment illustrated in FIGS. 6( a) and 6(b), the surface of a metal mesa structure 648 of a metal core printed circuit board 640 is higher than that of the first and second contact pads 616 a and 616 b of a light emitting diode chip 630, a thinner passivation layer 618 is formed to allow the metal mesa structure 648 physically contact the passivation layer 618.

In another embodiment, the passivation layer 318 illustrated in FIG. 3( f) may have a lower surface than that of the contact pads 316 a and 316 b. A passivation layer 718 having a lower surface is illustrated in FIG. 7( a). In this embodiment, a reflective layer 720 may be deposited to cover at least a portion of a passivation layer 718 and to reflect light toward the substrate 302, as illustrated in FIG. 7( b). The reflective layer 720 may include at least one of the reflective materials that have light reflection properties, such as Ag, Al, Rh, Ti, Ni, W, Mo, Cr, Pt and Pd. A second passivation layer 722 may then be deposited to cover the reflective layer 720, as shown in FIG. 7( c) and followed by applying a photolithography process to selectively remove part of the passivation material from the first and second contact pads 316 a and 316 b and obtain a desired thickness of the second passivation layer 722. The passivation layer 722 may have different thickness depending on the application.

In one embodiment as illustrated in FIG. 7( c), the surface of the passivation layer 722 may be at the same plane level as that of the first and second contact pads 316 a and 316 b. An additional layer, such as an adhesion layer, a seed layer or a buffer layer (not shown) may be sandwiched between the passivation layer 718 and the reflective layer 720 depending on the strength of the adhesion between the reflective and passivation materials. Similar to the assembly process described in FIG. 3( g), subsequent to the deposition of the passivation layer 722, the substrate may be chemically or mechanically polished to a desired thickness. The wafer may be diced into individual light emitting diode chip, resulting in a plurality of light emitting diode chips per wafer. As illustrated in FIG. 7( d), a light emitting diode chip 730 is flipped over so that contact pads 316 a and 316 b face down. To attach the flip light emitting diode chip 730 onto a metal core printed circuit board 740, conductive bonder 732 are re-melted to produce an electric connection between the contact pads (316 a, 316 b) of the light emitting diode chip 730 and the conductive pads (742 a, 742 b) of the metal core printed circuit board 740 using one of a reflow solder process, a thermal cure, an ultrasonic and ultraviolet methods, or any other suitable method. On the top surface of the metal core printed circuit board 740 and between the two conductive pads 742 a and 742 b, a metal mesa structure 748 may physically contact the passivation layer 722 resulting in an acceleration of heat dissipation from the flip light emitting diode chip 730 to the metal core printed circuit board 740 in operation.

Similar to the metal core printed circuit board 340′ shown in FIG. 3( h), a metal core printed circuit board 740′ has no metal mesa structure on its top surface as shown in FIG. 7( e). A space may exist between the flip light emitting diode chip 730 and the metal core printed circuit board 740′. To couple the flip light emitting diode chip 730 to the metal core printed circuit board 740′ dielectric thermal-conductive material 744 may be filled in the space to improve thermal dissipation. Alternatively, the coupling between a flip light emitting diode chip and a metal core printed circuit board may be made by altering the thickness of any or all of the first passivation layer 718, the reflective layer 720 and the second passivation layer 722 during the deposition and photolithography process. Example embodiments of altering thickness of the second passivation layer 722 are illustrated by FIGS. 8( a)-8(b) and FIGS. 9( a) and 9(b).

With reference to FIGS. 8( a) and 8(b), a metal core printed circuit board 840 having a metal mesa structure 848 with a lower surface than that of the first and second contact pads 316 a and 316 b may be assembled to a light emitting diode chip 830 having a thicker second passivation layer 822. With reference to FIGS. 9( a) and 9(b), a metal core printed circuit board 940 having a metal mesa structure 948 with a higher surface than that of the first and second contact pads 316 a and 316 b, may be assembled to a light emitting diode chip 930 having a thinner second passivation layer 922.

The passivation layers, such as the passivation layers 318, 518, 618 and 718 and the second passivation layers 322, 722, 822 and 922 may include passivation material such as SiO₂, Si₃N₄, Al₂O₃, AN, TiO or Ta₂O₅.

FIGS. 10( a)-10(c) are cross-sectional views to illustrate a method of fabricating a flip light emitting diode chipset 1000 according to one example embodiment of the present invention. The light emitting diode chipset 1000 including a plurality of light emitting diode dies, such as a light emitting diode die 1030 a and a light emitting diode die 1030 b. Each light emitting diode die is not limited to having a single passivation layer. The surface of the most upper layer is not limited to being at the same plane level as that of contact pads of each light emitting diode chip. In this embodiment, in order to describe concisely and briefly, the light emitting diode dies 1030 a and 1030 b are fabricated using the same fabrication process described in FIGS. 3( a)-3(f). Other fabrication processes described above may be used.

Referring to FIG. 10( a), the space 312 formed in FIG. 3( c) may separate the first light emitting diode die 1030 a from the second light emitting diode die 1030 b. The passivation layer 318 deposited over the wafer may cover sidewall 1032 and bottom wall 1034 of the space 312. A photolithography process may be applied to remove part of the passivation layer 318 on the sidewall 1032 of the space 312 to expose part of the sidewall of the second contact pad 316 b of the first light emitting diode die 1030 a and part of the sidewall of the first contact pad 316 a of the second light emitting diode die 1030 b, as illustrated in FIG. 10( b). As shown in FIG. 10( c), a layer of conductive material may then be deposited to cover the surface of the passivation layer 318 in the space 312 thus electrically connecting the second contact pad 316 b of the first light emitting diode die 1030 a to the first contact pad 316 a of the second light emitting diode die 1030 b. A passivation layer 1018 may be applied over the second contact pad 316 b of the first light emitting diode die 1030 a, surface of the conductive material in the space 312 and the first contact pad 316 a of the second light emitting diode die 1030 b, as shown in FIG. 10( d). Hence, adjacent light emitting diode dies are electrically connected. A light emitting diode chipset is obtained. The light emitting diode chipset may be assembled to a metal core printed circuit board (not shown) by connecting a plurality of the first and second conduct pads 316 a and 316 b to a plurality of first and second conductive pads (not shown) of the metal core printed circuit board, respectively.

FIGS. 11( a) and 11(b) illustrate chip on board assemblies according to example embodiments of the present invention. As illustrated in FIG. 11( a), contact pads 1116 a and 1116 b of a light emitting diode chip 1130 face down. To attach the flip light emitting diode chip 1130 onto a metal core printed circuit board 1140, conductive bonders (not shown) are re-melted to produce an electric connection between the contact pads (1116 a, 1116 b) of the light emitting diode chip 1130 and conductive pads (1142 a, 1142 b) of the metal core printed circuit board 1140 using one of reflow solder process, thermal cure, ultrasonic and ultraviolet methods or any other suitable methods. The flip light emitting diode chip 1130 may physically contact the metal core printed circuit board 1140 as illustrated in FIG. 11( a). Alternatively, dielectric thermal-conductive material 1144 may be filled in a space between the flip light emitting diode chip 1130 and the metal core printed circuit board 1140, as illustrated in FIG. 11( b), to improve thermal dissipation.

Many modifications and other example embodiments set forth herein will come to mind to which these example embodiments pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the embodiments are not to be limited to the specific ones disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions other than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

That which is claimed:
 1. A method of fabricating a light emitting diode device, comprising: providing a substrate; growing an epitaxial structure on the substrate, the epitaxial structure including a first layer on the substrate, an active layer on the first layer and a second layer on the active layer; depositing a conductive and reflective layer on the epitaxial structure; forming a group of first trenches and a second trench, each of the first and second trenches extending from surface of the conductive and reflective layer to the first layer to expose part of the first layer; and depositing conductive material to cover a portion of the conductive and reflective layer to form a first contact pad, and surfaces between adjacent first trenches to form a second contact pad, wherein the second contact pad electrically connects the first layer by filling the conductive material in the first trenches, and wherein the first contact pad is spatially separated from the second contact pad by the second trench.
 2. The method of claim 1, further comprising applying a photolithography process to transfer patterns on a photomask to the conductive and reflective layer and selectively remove parts of the first layer, the active layer, the second layer and the conductive and reflective layer to form the first and second trenches, wherein the patterns include at least one of columns, rows, grids and meshes.
 3. The method of claim 1, further comprising applying a photolithography process subsequent to the deposition of the conductive material to selectively remove parts of the conductive material to form the first and second contact pads.
 4. The method of claim 1, further comprising depositing a first passivation layer over the light emitting diode device subsequent to forming the first and second contact pads, the passivation layer including a first passivation material, applying a photolithography process to remove the first passivation material from the first and second contact pads and to obtain a desired thickness of the first passivation layer.
 5. The method of claim 4, further comprising applying a planarization process to the first passivation layer to make the first passivation layer planarized with the first and second contact pads.
 6. The method of claim 4 further comprising depositing a reflective layer to cover a portion of the first passivation layer, the reflective layer including reflective material having reflective properties.
 7. The method of claim 6, further comprising depositing one of an adhesion layer, a seed layer and a buffer layer prior to the deposition of the reflective layer.
 8. The method of claim 6 further comprising depositing a second passivation layer subsequent to the deposition of the reflective layer, the second passivation layer including a second passivation material, applying a photolithography process to remove the second passivation material from the first and second contact pads and obtain a desired thickness of the second passivation layer.
 9. The method of claim 1, further comprising depositing one of adhesion layer, seed layer or buffer layer to the substrate prior to one of steps of growing the epitaxial structure, depositing the conductive and reflective layer and depositing the conductive material to form the contact pads.
 10. The method of claim 1, further comprising applying a photolithography process to selectively remove parts of the epitaxial structure and the conductive and reflective layer to form at least one space prior to forming the first and second trenches, wherein the at least one space extends from surface of the conductive and reflective layer to the substrate to expose part of the substrate and separates a first light emitting diode die from a second light emitting diode die.
 11. The method of claim 10, further comprising depositing a first passivation layer over the light emitting diode device subsequent to forming the first and second contact pads, the first passivation layer covering side wall and bottom wall of the space, applying a photolithography process to selectively remove the first passivation material from the first and second contact pads and to obtain a desired thickness of the first passivation layer, and part of the first passivation layer on side wall of the space to expose part of side wall of a second contact pad of the first light emitting diode die and part of side wall of a first contact pad of the second light emitting diode die.
 12. The method of claim 11, further comprising grinding the substrate to a desired thickness, obtaining the first light emitting diode die and the second light emitting diode die by dicing, and coupling the first passivation layer to a metal mesa of the metal core printed circuit board.
 13. The method of claim 11, further comprising depositing the conductive material to cover surface of the first passivation layer in the space to allow the second contact pad of the first light emitting diode die electrically connect to the first contact pad of the second light emitting diode die.
 14. The method of claim 13, further comprising depositing a second passivation layer over the second contact pad of the first light emitting diode die, surface of the conductive material in the space and the first contact pad of the second light emitting diode die.
 15. The method of claim 14, further comprising grinding the substrate to a desired thickness, obtaining the first light emitting diode die and the second light emitting diode die by dicing, and coupling the second passivation layer to a metal mesa of the metal core printed circuit board.
 16. A light emitting diode device comprising: a substrate; an epitaxial structure grown on the substrate, the epitaxial structure including a first layer having a first material; an active layer on the first layer, the active layer having a second material; a second layer on the active layer, the second layer having the first material, the first layer and the second layer including different types of doping, the first material having wider band gap than that of the second material; a conductive layer deposited on the epitaxial structure; a first contact pad formed on the conductive layer; and a second contact pad covering surfaces between adjacent first trenches, the first and second trenches extending from the conductive layer to the first layer to expose part of the first layer, wherein the second contact pad electrically connects to the first layer by filling conductive material in the first trenches, and wherein the first contact pad is spatially separated from the second contact pad by a second trench.
 17. The light emitting diode device of claim 16, wherein the first and second trenches are formed by applying a photolithography process to transfer patterns on a photomask to the conductive layer and selectively remove parts of the epitaxial structure and the conductive layer to form the first and second trenches, wherein the patterns include at least one of columns, rows, grids and meshes.
 18. The light emitting diode device of claim 16 further comprises one of an adhesion layer, a seed layer and a buffer layer, wherein the one of the adhesion layer, seed layer and buffer layer is sandwiched between the substrate and the epitaxial structure, or between the conductive layer and the second layer.
 19. The light emitting diode device of claim 16, wherein the substrate includes at least one of Al₂O₃, SiC, ZnO, MgO, Ga₂O₃, AlGaN, GaLiO, MLA) and Si.
 20. The light emitting diode device of claim 16, wherein the first and second layer includes at least one of gallium nitride and gallium arsenide.
 21. The light emitting diode device of claim 16, wherein the active layer includes at least one of indium gallium nitride, AlGaAs, GaP, AlInGaP and GaAsP.
 22. The light emitting diode device of claim 16, wherein the conductive layer includes at least one of Ag, Al, Rh, Ti, Ni, W, Mo, Cr, Pt and Pd or one of In₂O₃, SnO₂, IMO, ZnO, IZO, ITO, Ni, Au, Ti and Ni.
 23. The light emitting diode device of claim 16, wherein at least one of the first and second contact pads includes at least one of Ti, Ni, Au, Cr and Ag.
 24. The light emitting diode device of claim 16, further comprising one of an adhesion layer, a seed layer and a buffer layer sandwiched between the epitaxial structure and the conductive layer, wherein the adhesion layer, the seed layer and the buffer layer includes at least one of Ti, Ni, Sb, Cr and WTi.
 25. The light emitting diode device of claim 16, further comprising a first passivation layer covering a portion of the conductive layer, side wall and bottom wall of the second trench, wherein surface of the first passivation layer is at the same plane level as, higher or lower than that of the first and second contact pads and wherein the second passivation layer includes at least one of SiO2, Si₃N₄, Al₂O₃, AlN, TiO and Ta₂O₅.
 26. The light emitting diode device of claim 25, further comprising a reflective layer deposited on the first passivation layer, wherein the reflective layer includes at least one of Ag, Al, Rh, Ti, Ni, W, Mo, Cr, Pt and Pd.
 27. The light emitting diode device of claim 26, further comprising a second passivation layer covering the reflective layer, wherein surface of the second passivation layer is at the same plane level as, higher or lower than that of the first and second contact pads and wherein the second passivation layer includes at least one of SiO2, Si₃N₄, Al₂O₃, AlN, TiO and Ta₂O₅.
 28. A method of assembling a light emitting diode device of claim 16 to a metal core printed circuit board, the method comprising: coupling the first and second contact pads of the light emitting diode device to first and second conductive pads of the metal core printed circuit board respectively; coupling a most upper layer to a mesa structure of the metal core printed circuit board.
 29. The method of claim 28, wherein the first and second contact pads of the light emitting diode device are electrically connected to the first and second conductive pads of the metal core printed circuit board by means of one of conductive bonders, conductive epoxy and solder paste.
 30. The method of claim 28, wherein the first and second contact pads of the light emitting diode device are coupled to the first and second conductive pads of the metal core printed circuit board by means of one of reflow solder process, thermal cure, ultrasonic and ultraviolet methods.
 31. The method of claim 28, wherein the most upper layer is coupled to the mesa structure by filling dielectric thermal conductive epoxy in a space between the most upper layer and the mesa structure. 